Aspects of Protonic Ionic Liquid as Electrolyte in Thermoelectric Generators

• Published in: Journal of electronic materials 2016-07, Vol.45 (7), p.3383-3389
• Main Authors: Laux, Edith, Uhl, Stefanie, Journot, Tony, Brossard, Julien, Jeandupeux, Laure, Keppner, Herbert
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Electrodes; Electrolytes; Electronics and Microelectronics; Generators; Instrumentation; Materials Science; Optical and Electronic Materials; Solid State Physics
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-016-4526-1

The Seebeck coefficient ( S E ) or thermopower and power output have been measured in a series of 16 ionic liquids (ILs). Thermoelectric current extraction is assisted by a dissolved redox couple (I 2 /LiI) added to the IL. The experiments were carried out in a thermoelectric cell where the IL is packaged between two electrodes. A large range of Seebeck coefficients and power outputs could be observed. The highest S E was measured for protonic ILs, reaching a value of 968  μ V/K. Moreover, the maximal power output of an IL-based thermoelectric generator and the polarity of its electrodes depend on the concentration of the redox-active species in the IL. The power output of the generator increased continuously with the redox concentration up to a maximum value (at 0.4 mol/L) but decayed for higher concentrations. We showed that an IL with high S E [linked to open-circuit voltage ( V OC )] does not necessarily lead to high power output; rather, it is carrier transport and extraction that determine the generator power. Surprisingly, the carrier extraction is not highest at the maximum electrode temperature difference; the power output observed for a given electrode temperature difference can be further increased by heating up the cold electrode in spite of the consequent reduction in the total temperature difference between the electrodes.